This invention relates to the field of light modulators. More particularly, this invention relates to the field of light modulators where an incident light is modulated to produce a blazed diffraction.
Bloom et al. in U.S. Pat. No. 5,311,360, entitled xe2x80x9cMethod and apparatus for modulating a light beam,xe2x80x9d teach a grating light valve which operates in a reflection mode and a diffraction mode. The grating light valve includes elongated elements suspended above a substrate. In the reflective mode, reflective surfaces of the grating light valve cause incident light to constructively combine to form reflected light. In the diffractive mode, the reflective surfaces of the grating light valve are separated by a quarter wavelength of the incident light to produce diffracted light. When the grating light valve is in the diffractive mode, the grating light valve predominantly diffracts light into a plus one diffraction order and a minus one diffraction order but also diffracts a small amount of light into higher diffraction orders.
Bloom et al. further teach an alternative grating light valve which operates in the reflection mode and in a blazed diffraction mode. The alternative grating light valve includes the elongated elements suspended above the substrate. For the alternative grating light valve, the elongated elements include off-axis neck portions at ends of each of the elongated elements. In the reflection mode, the elongated elements are parallel causing incident light to reflect from the elongated elements and, thus, produce the reflected light. In the blazed diffraction mode, each of the elongated elements is rotated about an axis defined by the off-axis neck portions to produce a blazed diffraction.
Because the light modulator is switched between the reflection mode and the blazed diffraction mode and because the reflection mode diffracts small quantities of light into the same angles as does the blazed diffraction mode, a contrast between the nonactivated state and the activated state is less than an optimum contrast. Further, the off-axis neck portions are critical to operation of the light modulator which necessitate tight tolerances for the off-axis neck portions making the light modulator relatively difficult to fabricate and also relatively expensive to fabricate.
What is needed is a blazed diffractive light modulator which provides higher contrast.
What is needed is a blazed diffractive light modulator which is easier to fabricate.
What is needed is a blazed diffractive light modulator which is more economical to fabricate.
The present invention is a light modulator. The light modulator includes elongated elements arranged parallel to each other and suspended above a substrate. The light modulator operates in a first diffraction mode and in a second diffraction mode. In the first diffraction mode, an incident light diffracts into at least two diffraction orders. In the second diffraction mode, the incident light diffracts into a single diffraction order, which is at a diffraction angle different from diffraction angles for the at least two diffraction orders.
Each of the elongated elements comprises a central blazed portion, a first outer blaze transition, and a second outer blaze transition. The central blaze portion couples the first outer blaze transition to the second outer blaze transition. Each of the central blazed portions comprises a reflective surface. Selected ones of the central blazed portions comprise a first conductive element. The first outer blaze transition and the second outer blaze transition are coupled to the substrate. The substrate comprises a second conductive element.
The elongated elements produce the first diffraction when a first electrical bias, preferably a zero electrical bias, is applied between the first conductive elements of the selected ones of the elongated elements and the second conductive element. A relative height of the blazed portions are adjusted to produce the second diffraction when a second electrical bias is applied between the first conductive elements of the selected ones of the elongated elements and the second conductive element.